1. Field of the Invention
The present invention relates to the heat dissipation structure of a power transmitting/receiving antenna for use in a wireless power transfer system for charging, supplying or collecting energy by a non-contact method.
2. Description of the Related Art
Non-contact wireless energy transfer technologies have attracted increasing attention these days in order to increase the mobility and waterproofness or dustproofness of various electronic devices as much as possible. This is because by transmitting electric power by such a non-contact method, various wireless consumer electronic appliances such as a wireless wall-mounted TV monitor are realized and a big moving object such as an electric car can be easily charged and supplied with electric power.
As a novel non-contact power transfer method that would replace the conventional one that uses electromagnetic induction, a resonant magnetic coupling method has been proposed in United States Patent Application Laid-Open Publication No. 2008/0278264-A1, for example. According to such a method, resonance mode coupling between resonators is used to realize longer-range and higher-efficiency power transfer than the conventional electromagnetic induction method. They believe that particularly if a resonant magnetic field is used, influence on surrounding organisms would be reduced compared to a situation where a resonant electric field is used.
Meanwhile, part of the loss that has been caused by such a resonant magnetic coupling type power transfer system turns into heat in the resonator. The heat that has been generated by the resonator affects the temperature characteristic of the resonator itself or its surrounding circuits so much as to decrease the transfer efficiency eventually. Particularly when a huge electric power is transmitted, a significant quantity of heat will be generated, and therefore, the heat that has been generated by the resonator should be dissipated due to safety considerations, too.
As for a structure for dissipating the heat, a heat dissipation structure for use in a non-contact power supply device of an electromagnetic induction type is disclosed in Japanese Patent Application Laid-Open Publication No. 2008-087733, for example. That heat dissipation structure is designed to dissipate heat by coating the surface of primary and secondary coils and that of primary and secondary magnetic cores with a thermal conductor that is electrically insulating and not affected by electromagnetic field.
Japanese Patent Applications Laid-Open Publications No. 2009-004513 and No. 2006-129605 disclose another heat dissipation technique applicable to an electromagnetic induction type power supply device. According to that technique, heat is dissipated by bringing a heat dissipation structure, which is made of a metallic conductor, into close contact with the surface of an inductor.
Furthermore, Japanese Patent Application Laid-Open Publication No. 2005-108654 discloses a technique for cooling an excitation coil by providing a cooling member at the core of a Litz wire, which has been formed by twisting together a number of fine conductive wires. According to that patent document, examples of the cooling members include a PDA based polymer materials with high thermal conductivity, a resin to which carbon-based filament has been added, aluminum and heat pipe.
According to the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2008-087733, the heat dissipation structure is made of an electrical insulator, which ordinarily has a lower thermal conductivity than an electrical conductor. That is why the degree of heat dissipation achieved is lower than when an electrical conductor is used to make the heat dissipation structure.
On the other hand, according to the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2009-004513, an electrical conductor, which usually has a higher thermal conductivity than an electrical insulator, is used as a material for the heat conducting layer, and therefore, the degree of heat dissipation achieved is no longer low. However, the heat is dissipated with the heat dissipating end of the heat conducting layer kept in close contact with either the ground of its internal circuit or the housing connected to the ground without subjecting that end to any insulation treatment. Thus, the electrically conductive heat conducting layer forms an electrically closed loop. As a result, due to the magnetic field generated while electric power is being transmitted, induced current will flow through the heat conducting layer, thus causing electrical conduction loss. Consequently, according to the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2009-004513, the power transfer efficiency decreases.
Japanese Patent Application Laid-Open Publication No. 2006-129605 does disclose a heat dissipation structure that does not form such an electrically closed loop. However, since the heat dissipation structure is supposed to be arranged on the surface of an inductor, which generates heat, the degree of heat dissipation achieved could be low if the inductor either had a large turn number or were relatively thick.
Furthermore, with the heat dissipation structure disclosed in Japanese Patent Application Laid-Open Publication No. 2005-108654 adopted, the heat dissipation effect should be increased by the cooling member that is arranged in close contact with multiple conductive wires. However, if the cooling member is made of an electrical conductor, induced current will also be generated and the power transfer efficiency may also decrease as in Japanese Patent Application Laid-Open Publication No. 2009-004513 mentioned above.
It is therefore an object of the present invention to provide a heat dissipating technique for dissipating the heat, which has been generated by a resonator for use in a resonant magnetic coupling type wireless power transfer system, with the decrease in power transfer efficiency minimized.